In recent years, adjustable-speed operation of the motors (rotating electric machines) each using an inverter is prevalent in terms of energy saving. However, when a motor is driven by an inverter that generates a rectangular-wave voltage, if a steep-fronted surge voltage is generated by the inverter and causes a high voltage between the motor coil turns, this could result in insulation deterioration between the coil turns (refer to Non-Patent Reference 1).
Regarding this turn-to-turn insulation deterioration problem, Non-Patent Reference 2 proposes a method of strengthening the turn-to-turn insulation by, for example, increasing the thickness thereof in addition to reducing the number of turns of the lead wire forming a first coil to which the surge voltage from the inverter is applied. However, as described in Non-Patent Reference 2, insulation strengthening has had its limits since the rotating electric machine changes in mechanical output characteristics.
Also, Non-Patent Reference 3 discloses designing a rotating electric machine for reduced capacitance between a turn and a core, against the capacitance between turns, in order to improve the turn-to-turn insulation distribution.
In addition, Patent Reference 1 proposes a method of alleviating a turn-to-turn voltage share in a high-voltage rotating electric machine by connecting a capacitor for adjusting distributed capacitance between turns, from the external section of a winding.
[Patent Reference 1: Japanese Patent Laid-open No. Sho 50(1975)-301 (JP-A-1975-301), What is Claimed is, FIGS. 3, 6]
[Non-Patent Reference 1: IEEJ Technical Report, Vol. 739, pp. 14-20, issued in August 1999] (IEEJ: Institute of Electrical Engineers of Japan)
[Non-Patent Reference 2: “Characterization Tests on Induction Motor with Reduced Number of Terminal Coil Turns”, material for technical presentation in the IEEJ Rotating Machines Working Group, RM-00-92 to RM-00-109, p. 19, Hitosugi Kazuyoshi, Shoji Moriyasu]
[Non-Patent Reference 3: “Modern High-Voltage Engineering”, pp. 91-93, written by Uchida Masayuki, published by Ohmsha, Ltd.]